Java's support for parallel and distributed processing makes the language attractive for metacomputing applications, such as parallel applications that run on geographically distributed (wide-area) systems. To obtain actual experience with a Java-centric approach to metacomputing, we have built and used a high-performance widearea Java system, called Manta. Manta implements the Java RMI model using different communication protocols (active messages and TCP/IP) for different networks. The paper shows how widearea parallel applications can be expressed and optimized using Java RMI. Also, it presents performance results of several applications on a wide-area system consisting of four Myrinet-based clusters connected by ATM WANs. 1 Introduction Metacomputing is an interesting research area that tries to integrate geographically distributed computing resources into a single powerful system. Many applications can benefit from such an integration [11, 22]. Metacomputing systems support such...

We are developing a distributed computing environment based on virtual machines featuring application monitoring, network monitoring, and an adaptive virtual network. In this paper, we describe our initial results in monitoring the communication traffic of parallel applications, and inferring its spatial communication properties. The ultimate goal is to be able to exploit such knowledge to maximize the parallel efficiency of the running parallel application by using VM migration, virtual overlay network configuration and network reservation techniques, which are a part of the distributed computing environment. Specifically, we demonstrate that: (1) we can monitor the parallel application network traffic in our layer 2 virtual network system with very low overhead, (2) we can aggregate the monitoring information captured on each host machine to form a global picture of the parallel application's traffic load matrix, (3) we can infer from the traffic load matrix the application topology. In earlier work, we have demonstrated that we can capture the time dynamics of the applications. We begin here by considering offline traffic monitoring and inference as a proof of concept, testing it with a variety of synthetic and actual workloads. Next, we describe the design and implementation of our online system, the Virtual Topology and Traffic Inference Framework (VTTIF), and evaluate it using a NAS benchmark.

Metacomputing infrastructures couple multiple clusters (or MPPs) via wide-area networks and thus allow parallel programs to run on geographically distributed resources. A major problem in programming such wide-area parallel applications is the difference in communication costs inside and between clusters. Latency and bandwidth of WANs often are orders of magnitude worse than those of local networks. Our MagPIe library eases wide-area parallel programming by providing an efficient implementation of MPI's collective communication operations. MagPIe exploits the hierarchical structure of clustered wide-area systems and minimizes the communication overhead over the WAN links. In this paper, we present improved algorithms for collective communication that achieve shorter completion times by simultaneously using the aggregate bandwidth of the available wide-area links. Our new algorithms split messages into multiple segments that are sent in parallel over different WAN links, thus resulting ...

Virtual machine grid computing greatly simplifies the use of widespread computing resources by lowering the level of abstraction, benefiting both resource providers and users. For the user, the Virtuoso middleware that we are developing closely emulates the existing process of buying, configuring and using machines. VNET, a component of Virtuoso, is a simple and e#cient layer two virtual network tool that makes these virtual machines appear to be connected to the home network of the user, simplifying network management. Overlays like VNET have great potential as the mechanism for adaptation. Here, we describe our second generation VNET implementation, which includes support for arbitrary topologies and routing, application topology inference, and adaptive control of the overlay. We demonstrate that the performance of unmodified applications, in particular bulk synchronous parallel applications running inside the virtual machines and serviced by VNET, can be significantly (up to a factor of two) enhanced by adapting the VNET topology and forwarding rules on the fly based on intelligent application tra#c inference methods. The adaptation scheme requires no knowledge or participation from the user or application developer.

Java’s support for parallel and distributed processing makes the language attractive for metacomputing applications, such as parallel applications that run on geographically distributed (wide-area) systems. To obtain actual experience with a Java-centric approach to metacomputing, we have built and used a high-performance wide-area Java system, called Manta. Manta implements the Java Remote Method Invocation (RMI) model using different communication protocols (active messages and TCP/IP) for different networks. The paper shows how widearea parallel applications can be expressed and optimized using Java RMI. Also, it presents performance results of several applications on a wide-area system consisting of four Myrinetbased clusters connected by ATM WANs. We finally discuss alternative programming models, namely object replication, JavaSpaces, and MPI for Java.

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The emergence of meta computers and computational grids makes it feasible to run parallel programs on large-scale, geographically distributed computer systems. Writing parallel applications for such systems is a challenging task which may require changes to the communication structure of the applications. MPI's collective operations (such as broadcast and reduce) allow for some of these changes to be hidden from the applications programmer. We have developed MAGPIE, a library of collective communication operations optimized for wide area systems. MAGPIE 's algorithms are designed to send the minimal amount of data over the slow wide area links, and to only incur a single wide area latency. This paper discusses MPI's collective reduction operations. Compared to systems that do not take the topology into account, such as MPICH, large performance improvements are possible. For larger messages, best performance is achieved when the reduction function is associative. 1 Introduction Severa...

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this paper, we present a novel methodology for improving the performance and dependability of application-level messaging in Grid systems. Based on the Network Weather Service, our system uses non-parametric statistical forecasts of requestresponse times to automatically determine message timeouts. By choosing a timeout based on predicted network performance, the methodology improves application and Grid service performance as extraneous and overly-long timeouts are avoided. We describe the technique, the additional execution and programming overhead it introduces, and demonstrate the effectiveness using a wide-area test application

Heterogeneous computing environments are becoming an increasingly popular platform for executing parallel applications. Such environments consist of a diverse set of machines and offer considerably more computational power at a lower cost than a parallel computer. Efficient heterogeneous parallel applications must account for the differences inherent in such an environment. For example, faster machines should possess more data items than their slower counterparts and communication should be minimized over slow network links. Current parallel applications are not designed with such heterogeneity in mind. Thus, a new approach is necessary for designing efficient heterogeneous parallel programs.